Hilton, 26, who, with her parents Kathy and Rick Hilton, was present in the Los Angeles Metropolitan courtroom, looked stunned when the sentence was handed down. Her mother gasped.

"I'm shocked and disappointed at the sentence by the judge," the hotel heiress's attorney, Howard Weitzman, said afterwards. "To sentence Paris Hilton to jail is uncalled for, inappropriate and ludicrous. She was singled out for who she is. She's been selectively targeted. Paris was honest in her testimony. We plan to appeal. Shame on the system."

Sauer ordered Hilton to report to jail no later than June 5.

In the course of the two-hour hearing, Hilton took the witness stand and claimed that her rep, Elliot Mintz, had repeatedly informed her that her license had been suspended for only 30 days and that she could still drive for work-related matters.

"I never would've been driving if my license was suspended," she testified. "I follow the law. I'm followed by cameras every single day."

Before sentence was delivered, Hilton stood to give a statement to the judge, saying, "I respect the law. ... I want you to know I'm very sorry and will pay complete attention to everything from now on."

But prosecutors who sought the 45-day term for Hilton contended that on Feb. 27 she knowingly drove despite the suspension, and that she failed to enroll in an alcohol-education program by her deadline of Feb. 12. (By April 17 she still had not signed up, said prosecutors.)

In their case against her, prosecutors called to the stand three law-enforcement officers who had individually pulled over Hilton on three occasions, starting with her DUI arrest in September 2006. The first officer warned her that her license might be suspended as a result of the DUI; the subsequent two officers informed her this was definitely the case.

After hearing the arguments from both sides, Judge Sauer singled out what he referred to as the "smoking gun" – a written warning Hilton received and signed on Jan. 15 after being pulled over by the California Highway Patrol, verifying that, indeed, her license was suspended.